Thermostatic switch



Feb. 3, '1931. w, A RANKlN 1,791,225

THERMOSTATIC SWITCH Filed Nov. 7. 1928 @Wwf/uf., lL-ATTO EY Patented Feb. 3, 1931 UNITED STATES PATENT OFFICE WILLIAM.' A. RANKIN, OF TOLEDO, OHO, ASSIGNO-R TO ROBESON-ROCHESTER CORPORA- TION, 0F ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK i THERMOSTATIC SWITCH Application led November 7, 1928. Serial No. 317,748.

This invention relates to a thermostatic switch of the type adapted to open an electrical circuit when a. predetermined temperature is reached. It has for its principal object the provision of a simple and elicient y provision of a quick acting thermostatic switch, in which the circuit is broken more rapidly than in other thermostatic switches heretofore used, so that less a-rcing occurs at the contacts.

Another object is the provision of a switch which may be easily adjusted to vary the temperature at which it will open, and which when once adjusted will remain set at the desired temperature. until al subsequent adj ustment is made.

To these and other ends the invention resides in certain improvements and combinations of parts, all as will be hereinafter more fully described, the novel features being pointed out in the claims at the end of the specification.

In the dra-wings:

Fig. 1 is a plan of a thermostatic switch constructed in accordance with a. preferred embodiment of the invention;

Fig. 2 is a side elevation thereof;

Fig. 3 is a longitudinal section taken centrally through the switch, showing the contacts in closed position;

Fig. 4 is a View similar to Fig. 3 showing the contacts in open position; v

Fig. 5 is a transverse section on the line j 5-5 of Figs. 2 and 3;

- when a Fig. 6 is a perspective view of one element of the switch, and

Fig. 7 is a perspective view of a stop member.

Similar reference numerals throughout the several views indicate the same parts.

A switch constructed according to the present invention may be used in connection with any apparatus in which it may be desired to open or close an electrical circuit predetermined temperature is reached. The switch comprises a supporting and heat transmitting member 11 which has pins 12 projecting from one side thereof, and is also provided with a. hole 13 in a lug 14, the pins and hole being useful in attaching the member to any desired part of the apparatus with which it is used.

A central passage 15 preferably extends through the member 11 and apart of the apparatus, such as the part whose heat is intended to control the thermostatie switch, may extend through this passage 15. Preferably, the member 11 is made of some material which is a` good conductor of heat, such as aluminum.

Mounted upon the supporting and heat transmitting member 11 in any suitable way, such as by the screws 16, is al bimetallicy heat responsive element 17, one end of which ex- .in the opposite direction from the end which carries the contact, and at this opposite end a stop member 20 and a resilient member 21 are attached to the element. The mode of attachment is best seen from Fig. 3, in Which it will be observed that rivets 22 pass through the element 17, the stop member 20, and the resilient member 21. Each of these rivets is surrounded by a bushing of insulating material, and a layer of insulating material 23 is placed between the stop member 22' and the element 17 another layer of insulation 24 being placed between the resilient member 21 and a plate 25 engaged by the heads of the rivets 22. Thus the stop member 20 and the resilient member 21 are insulated from the element 17 whenever the'switch is open.

The end of an electrical conductor 27 may be inserted between the members 20 and 21, as shown in Fig. 4, and thus serves as a spacing means for holding the members 2O and 21 a slight distance apart, as well as an electrical connection to the member 21. The other side of the electrical circuit may be connected in any suitable manner to the supporting and ylic heat transmitting member 11, which is connected in turn to the element 17.

A bimetallic element which will change its shape in respon-se to temperature variations is well understood, and need not be described in detail here. Any suitable material may be used for the element 17 The resilient member 21 carries an elec'- trical contact 28 adapted to cooperate with the contact 18 on the element 17. The resilient member is constructed so that itsv free end which carries the contact normally tends to move upwardly when viewed as in Figs. 2', 3 and 4, so that it tends to move its contact 28 against the contact 18.

When the element 17 is deflected by a rising temperature from its straight position illustrated in Fig. 3 to a curved shape or position as shown in Fig. 4, the contact 18 on 'the element is raised, and the contact 28, mounted on the resilient member 21 follows along with the contact 18 for a short distance until the resilient member comes into contact with the stop member 20. Further motion of the resilient member is thereby prevented, and continued bending of the element 17 draws the two contacts 18 and 28 apart, so that the switch is open.

The stop member 20, above alluded to, comprises a bar having one or more stilfening flanges extending through a portion of its length. In the embodiment shown, stilfening flanges 30 depend from opposite sides of the 'stop member, so as to form a channel with its open side downwardly, the resilient member 21 being received within this channel. Olfsets or grooves 31 ymay be formed in the channel near one end, these grooves assisting 1n retaining the insulating material 23 and 24 in place. .The stiifening flanges 30 prevent deformation of that portion of the stop member along which they extend, and also act as guideways for the resilient member 21, preventing accidental lateral deflection of this member.

The stifeningflanges 30 stop somewhat short of the free end ofthe stop member 20, as will be observed from Figs. 2 and 7,- and the free end 32 of the stop member is made of material which may be intentionally deformed at will, and yet which is sufliciently strong to withstand ordinary use, so that it will not be bent during the operation of the switch by coming in contact repeatedly with the resilient member 21,l but will continue to act as a rigid stop member to -control the position of the resilient member. It will be obvious from Figs. 3 and 4 that the position of the deformable end 32. of-A the stop member 20 limits the extent to which the contact 28 may follow along with the contact 18 when the element 17 bends, and therefore a chan e in the position of the end 32 will .change the point at which the switch will open. In this wav'- the temperature at which ythe switch opens or closes the circuit may be varied at will, by deforming the end 32 of the stop member 20 either when the switch is originally installed or at any subsequent time.

As is well understood by those skilled in the art, thermostatic switches of the types heretofore used ordinarily open rather slowly, and thus considerable arcing may occur at the contacts. Such arcing is undesirable for many-reasons, among which may be mentioned the overheating and destruction of the contacts, and the possibility of the arc causing damage to other parts of the apparatus in which the switch is used.

The present switch is designed to have a rapid action, much quicker than that of other switches heretofore known. Ordinarily, heat will be transmitted to the bimetallic element of the switch more rapidly through the material on which the switch is mounted, than through the air. This is especially true 1n the present instance, since the supporting member is made of material such as aluminum which is a good conductor of heat, and asthis supporting'V memberI preferably surrounds the part of the apparatus whose temperature is intended to control the switch, 1t follows that there is a direct heat conducting connection between the element 17 and the part of the apparatus whose heat should control the element.

It will be -observed that the heat conducting member 11 is connected to the element 17 not at one end, as has been customary in previous switches, but at a point spaced from each end of the element, and preferably near the middle thereof. Heat from the member 11 may therefore flow into the element 17 in both directions away from the supporting member. With this construction, the benad-` ing of the element in response to a glven rise in temperature is much more rapid than would occur if the heat transmitting member were attached to the element at one end.'

In operation, considering Fig. 4, the heat which flows from the member 11 into the right hand end of the'element 17 will causey this end of the element to bend somewhat, as shown.y In this figure the -line 35 indicates the vposition of the lower edge of the contact 18 when the element 17 is in its straight or undeflected position as shown in Fig. 3. The position of the contact 18 relative to the line 35 in Fig. 4 therefore shows the amount of 'opening of the switch which is caused by the bending of that part of the element 17, which extends rightwardly from the support 11. This is the yonly extent of opening which would exist in a thermostatic switch of the type heretofore known, under the same temperature conditions.

In the present switch, however, an addii tional increment of opening is caused by the fact that the, element 17 has its other end extended past the supporting member 1'1, and

the' other contact 28 of the switch is mounted on a member carried by this other or extended end of the element. Heat will How from the member 11 not only rightwardly into the' right hand end of the element 17 to cause the movement above mentioned, but will also flow leftwardly into the extended end of the element 17, and will thus cause the left end of this element to bend-from the Figure 3 position to the Figure 4 position. This upward bending of the extended end of the element 17 will cause a corresponding downward tilting of the cantilever stop member and the member 21 which carries the contact 28. Thus the contact -28 is lowered from the position shown in Fig. 3 to that illustrated in Fig. fi, the distance or extent of this lowering being indicated by the displacement of the contact 28 from the reference line 35.

Tt is seen that the distance by which the contact 28 is displaced from the reference line is approximately twice as great as the distance by which the contact 18 is displaced therefrom. This is caused by the relative lengths of the arms to which the contacts are attached. The motion of the contact 18 is due to the bending of the rightwardly extending arm of the element 17, which has a length equal to the distance from the contact 18 to the screws 16. Theleftwardly extending arm of the element 17 constitutes an arm of substantially the same length, and the left hand end will therefore be raised from its normal position to approximately the same extent as that to which the right hand end of the element 17 was raised.

Since the stop member 20 and member 21 are rigidly fastened to the left hand end of the element 17, they will 'be tilted downwardly to a degree corresponding to the inclination of the left hand end of this element. The stop member will control the tendency of the resilient member 21 to spring upwardly, and will depress the resilient member to the position shown in Fig. 4. Since the length of the arm 21 from its contact 28 to the point where it is attached to the element 17 is approximately twice as great as the length of the left hand or extended portion of the element 17 it follows that the displacement of the right hand end o f the member 21 will be approximately twice as great as the displacement of the left hand end of the element 17 which causes it. And as the displacement of the left end of the element 17 is approximately equal to the displacement of the right hand end of the element, it follows. that the right end of the contact-carrying member 21 is displaced approximately twice as much as the right endI of the element 17. Therefore, the contact 28 will be lowered from its undisplaced position, illustrated by the reference line 35 in Figure 4, approximately twice as much as the contact 18 will be raised above this line.

the right hand arm of the element 17. In

such a switch, the extent of opening would simply be the amount by which the contact 18 was raised above the reference line 35, as the contact 28 would be iixed relative to the supporting member 11 and would therefore remain at the position of this reference line 35.

If heat be supplied to the element 17 at some intermediate point, such as through the heat transmitting member 11, both ends of the element will commence their deflection simultaneously, and the contacts will be moved comparatively rapidly. It is obvious that if heat travels at a given linear rate per second through the bimetallic element, the whole length of this element will be heated much more quickly if the heat flows in both directions from an intermediate` point, than would be the case were the heat applied at one end of the element, as in the prior constructions. Thus the fact that the bimetallic element is extended in both directions from the supporting and heat transmitting member 11 results i-n a quick-acting thermostatic switch, as well as one in which the extent of opening is greater than in other thermostatic switches which do not utilize such an extension of the bimetallic element.

While one embodiment of the invention has been disclosed, it is to be understood that the inventive idea may be carried out in a number of ways. This application is therefore not to be limited to the precise details shown, but is intended to cover all variations and modifications thereof falling within the Y spirit of the invention or the scope of the appended claims.

I claim as my invention:

1. In a thermostatic switch, the combination with a support, of a bimetallic heat responsive element mounted thereon, one end of said element projecting in one direction from said support, an electrical contact carried by said end of said element at a point spaced from said support, said element having a portion extending from said support in the opposite direction from the end carrying said Contact, a member mounted on said extended portion of said element, and an electrical contact on said member adapted to cooperate with said contact on said element.

2. Tn a thermostatic switch, the combination with a support, of a bimetallic heat responsive element mounted thereon, one end of said element projecting in one direction from said support, an electrical contact carried by said end of said element at a point spaced from `said support, said element having a portion extending from said support in the opposite direction from the end carrying said contact, aresilient member mounted on said extended portion of said element, an electrical contact on said member adapted to cooperate with the contact on said element, said resilient member normally tending to move its contact into position to'engage the contact on said element, and a stop member also mounted on the extended portion of said element for controlling the position of said resilient member.

3. Ina thermostatic switch, the combination with a support, of a bimetallic heat responsive element mounted thereon, one end of said element projecting in one direction from said support, an electrical contact carried by said end of said element at a point spaced from said support, said element having a portion extending from said support in the opposite direction from the end carrying said contact, a resilient member mounted on saidv extended portion of said element, an electrical contact on said member adapted to cooperate with the Contact on said element, said resilient member normally tending to move its contact into position to engage the contact on said element, and a stop member also mounted on the .extended portion of said element between said element and said resilient member for controlling the position of said resilient member.

4. In a thermostatic switch, the combination with a support, of a bimetallic heat responsive element mounted thereon, an electrical contact carried by one end of said'element, a resilient member mounted on said element at a point spaced from said contact, an electrical con-tact on said resilient member adapted to cooperate with the contact on said element, said resilient member normally tending to move its contact into position to engage lthe first mentioned contact, and a stop member mounted between said element and said resilient member for controlling the position of the latter, said stop member having a stiffening flange throughout a portion of its length, and @other portion of said stop member being deformable' at will topermit adjustment of said stop member to vary its action upon said resilient member.

5. A quick-acting thermostatic switch comprising a bimetallic heat responsive element, an electrical contact near one end thereof, a contact carrying member mounted on said element near the other end thereof, a second electrical contact carried by said member and adapted to cooperate with said first named contact, and a member for supporting and transmitting heat to said bimetallic element, said member being attached tosaid element ata point spaced from each end of the latter so that heat from said member vmay liilow along said bimetallic element in two directions to produce comparatively rapidfmovement of said element;

, 6. In a thermostatic switch, the combination with a support, of a bimetallic heat responsive element mounted thereon, one end of said element projecting from said support, an electrical contact, a member carried by said projecting end of said element at a point spaced from said support, and an electrical contact mounted on said member and adapted to cooperate with said first named contact.

7. In a thermostatic switch, the combination with a bimetallic heat responsive member, of a contact-carrying member connected thereto, and a stop member for controlling the position of one of said members, said stop member comprising a channel shaped portion arranged to receive one of said members therein.

8. In a. thermostatic switch, the combination with a bimetallic heat responsiveelement, of a contact-carrying member connected thereto, and a stop member mounted between said element and said contact-carrying member for controlling the position of the latter, said stop member comprising a pair of iianges extending along opposite sides of said contact-carryingmember for preventing displacement thereof in one plane, and a portion for controlling the position of said contact-carrying member in another plane.

9. In a thermostatic switch, the combination with a bimetallic heat responsive element, of a contact-carryin member connected thereto, and a stop mem er for controlling the position of said contact-carrying member, said stop member comprising a portion suiiiciently strong to withstand ordinary operation but deformable at will to vary the action of said stop member on said contact-carrying member.

10. A stop member for use in a thermostatic switch, said member comprising a strip having marginal flanges arranged to form a channel and to stiffen said member, said flanges stopping `short of one end of said stri to leave a portion thereof unstiiiened an capable of intentional deformation.

I WILLIAM A. RANKIN.

lil-'S 

